Actinobacillus actinomycetemcomitans and Eikenella corrodens are suspected pathogens in periodontitis but both also occur in healthy individuals. This research plan will (1) examine the variabilities of clonal diversity and stability of these organisms within the host, (2) evaluate the synergism between these organisms in localized juvenile periodontitis, and (3) identify pathogenic clones within species. The degrees of clonal diversity of these organisms within the host vary among subjects. Juvenile periodontitis patients harbor greater numbers of distinct E. corrodens clones than healthy subjects; the differences may result from increased susceptibilities of the patients to repeated infections by exogenous clones. Repeated colonization/infection may result in a reduced clonal stability due to replacement of the resident clones by exogenous clones. Colonization/infection by one organism may predispose the host to colonization/infection by the other organism; the relationship is recognized as synergism between the organisms. Within A. actinomycetemcomitans and E. corrodens, strains associated with health may be relatively harmless while others recovered from infections may be more pathogenic. The objectives of this research plan are to: (1) Compare the degrees of clonal diversity, by AP-PCR, of subgingival A. actinomycetemcomitans and E. corrodens in periodontally healthy subjects and localized juvenile periodontitis patients. (2) Examine the clonal stability of subgingival A. actinomycetemcomitans and E. corrodens. Subjects will be sampled again in 9 and 18 months. A quantitative method will be used to assess and compare the clonal stabilities between subject groups. (3) Determine the correlations in the proportional levels or the degrees of clonal diversity between subgingival A. actinomycetemcomitans and E. corrodens. (4) Examine the genetic distinctions between A. actinomycetemcomitans and E. corrodens clones recovered from health and disease by serotyping, AP-PCR genotyping and mutilocus enzyme typing. The study subjects will be limited to Asian-Americans to avoid variations arising from using subjects with different ethnicities, and to examine an ethnic group which is under-represented in previous periodontal disease research. This research plan will provide crucial information regarding the significance of clonal diversity and stability of A. actinomycetemcomitans and E. corrodens in periodontal disease and the synergism between these two organisms, and identify virulent clonal types within these species. The information will be important for the (1) future studies of bacterial virulence factors and (2) prevention and treatment of periodontitis associated with these organisms.